In a telephone switching system a central office, hereinafter referred to as the host office, controls the routing and interconnection of calls not only among directly terminating customer lines but also among such lines as terminate at remote switching modules linked to the host office by pluralities of trunks. This switching system employs time-shared digital switches under stored program control including a central processor at the host office and a module processor at each remote center. Communication between the host office and the several remote offices for message, control and timing information is carried out on digital carrier trunks. Typically as many as twenty digital trunks can be accommodated between the host office and each remote module. Flexibility is incorporated into the trunking arrangement by providing for time slot interchanges among the available trunks under the direction of the stored program. Furthermore, operational reliability is assured by providing duplex facilities, each of which includes its own module processor, at each remote module.
Since a remote switching module can be located as far as one hundred miles from its host office, provision is made for stand-alone operation. In this type of operation the remote module is capable of handling all local interconnections among lines which it terminates, even when the host office link goes out of service. As long as the host office link is down, however, some specialized services may become unavailable. When full service is restored or whenever software integrity, i.e., coordination between the central processor at the host office and module processors at a remote office, comes into question, it may be necessary to reestablish control by the host office. On such an occasion it becomes necessary to reset and resynchronize the module processor with the central processor. To avoid an inadvertent false reset of the module processors at a remote module it has been found to be desirable that the reset order be transmitted in parallel through all operating links simultaneously and that the validity of the reset message be verified for consistency among the operating trunks.
The subject matter of this invention is concerned with an efficient circuit for determining that a majority has been achieved, i.e., a majority vote circuit, from a plurality of common signaling paths.
It is an object of this invention to determine that a majority of a selected subset of input signals is in agreement at a receiving location.
It is a further object of this invention to provide a majority vote circuit by a serial rather than a combinatorial implementation.